The preparation and use of slab-shaped gels for electrophoretic separations generally require delicate handling through a time-consuming sequence of manipulations by the laboratory technician. The gel is first cast in a mold, then transferred to a support or enclosure which allows the passage of electric current for electrophoresis. The mold of course must be leakproof, yet during electrophoresis the gel must have two opposing ends exposed to permit contact with buffer solutions in which the electrodes are placed. The transfer presents many opportunities for error and nonreproducibility, as well as the danger of ruining a gel and the loss of an analysis as well as valuable laboratory time. Subsequent to electrophoresis, the plates of the mold must be capable of being separated to permit staining of the gel, presenting further problems in leakproofing.
These problems are well illustrated by commercial products currently available for slab gel electrophoresis. A typical gel enclosure consists of two flat plates separated by spacers along two opposing longitudinal edges, the transverse edges remaining open, and the plates held together by compression along the longitudinal edges. To cast the gel between the two plates the assembled arrangement consisting of the plates, spacers, and whatever clamps are used to hold the plates and spacers together, are placed on a casting stand where one of the open edges of the plate assembly is pressed against a resilient sealing material such as rubber. The gel solution is then poured between the plates through the remaining open end. Once the gel has solidified, the plate assembly is removed from the casting stand and connected to appropriate components which permit the electrical connections needed for electrophoresis.
This procedure has several disadvantages. First, the plate assembly must be forced against the rubber surface with pressure to eliminate leakage. Second, an effective seal against the rubber surface also requires the plates and spacers to be carefully aligned and tightly compressed against each other. Such forces create a risk of disturbing the delicate gel, either during transfer from the casting stand to the cell which supplies the electrical connection, or during the final disassembly of the plates for removal and analysis of the gel. Third, the casting stand is an additional piece of equipment, raising the cost of the apparatus. Fourth, this multitude of manipulations and components makes the preparation and use of slab gels an expensive and cumbersome procedure, one which is not well suited to mass production or automation.